v. t. [ imp. & p. p. Invaded; p. pr. & vb. n. Invading. ] [ L. invadere, invasum; pref. in- in + vadere to go, akin to E. wade: cf. OF. invader, F. envahir. See Wade. ] [ 1913 Webster ]

1. To go into or upon; to pass within the confines of; to enter; -- used of forcible or rude ingress. [ Obs. ] [ 1913 Webster ]

Which becomes a body, and doth then invade
The state of life, out of the grisly shade. Spenser. [ 1913 Webster ]

2. To enter with hostile intentions; to enter with a view to conquest or plunder; to make an irruption into; to attack; as, the Romans invaded Great Britain. [ 1913 Webster ]

Such an enemy
Is risen to invade us. Milton. [ 1913 Webster ]

3. To attack; to infringe; to encroach on; to violate; as, the king invaded the rights of the people. [ 1913 Webster ]

4. To grow or spread over; to affect injuriously and progressively; as, gangrene invades healthy tissue.

Syn. -- To attack; assail; encroach upon. See Attack. [ 1913 Webster ]

v. i. To make an invasion. Brougham. [ 1913 Webster ]

n. One who invades; an assailant; an encroacher; an intruder. [ 1913 Webster ]

adj. same as invasive{ 1 }.
Syn. -- incursive, invasive. [ WordNet 1.5 +PJC ]

v. t. To insert as in a sheath; to produce intussusception in.

{ } a. (Biol.) (a) Sheathed. (b) Having one portion of a hollow organ drawn back within another portion. [ 1913 Webster ]

n. [ L. pref. in- + vagina sheath. ] [ 1913 Webster ]

1. (Biol.) The condition of an invaginated organ or part. [ 1913 Webster ]

2. The inward movement of the wall of a tissue or cell, to form a cavity; also, the cavity thus formed. [ PJC ]

3. Specifically: (Biol., Embryology) The inward movement of one part of the wall of a blastula, to form a gastrula; the process of gastrulation, in which layers of the ovum are differentiated. [ 1913 Webster +PJC ]

☞ In embolic invagination, one half of the blastosphere is pushed in towards the other half, producing an embryonic form known as a gastrula. -- In epibolic invagination, a phenomenon in the development of some invertebrate ova, the epiblast appears to grow over or around the hypoblast. [ 1913 Webster ]

n. [ L. invalescens, p. pr. of invalescere to become strong. See 1st In-, and Convalesce. ] Strength; health. [ Obs. ] [ 1913 Webster ]

a. Wanting health; valetudinary. [ R. ] [ 1913 Webster ]

n. [ F. invalide, n. & a., L. invalidus, a. See Invalid null. ] A person who is weak and infirm; one who is disabled for active service; especially, one in chronic ill health who is unable to care for himself. [ 1913 Webster ]

a. [ Pref. in- not + valid: cf. F. invalide, L. invalidus infirm, weak. Cf. Invalid infirm. ] [ 1913 Webster ]

1. Of no force, weight, or cogency; not valid; weak. [ 1913 Webster ]

2. (Law) Having no force, effect, or efficacy; void; null; as, an invalid contract or agreement. [ 1913 Webster ]

a. [ See Invalid, n. ] Not well; feeble; infirm; sickly; as, he had an invalid daughter. [ 1913 Webster ]

v. t. 1. To make or render invalid or infirm. “Invalided, bent, and almost blind.” Dickens. [ 1913 Webster ]

2. To classify or enroll as an invalid. [ 1913 Webster ]

Peace coming, he was invalided on half pay. Carlyle. [ 1913 Webster ]

v. t. [ imp. & p. p. Invalidated p. pr. & vb. n. Invalidating. ] [ From Invalid null. ] To render invalid; to weaken or lessen the force of; to destroy the authority of; to render of no force or effect; to overthrow; as, to invalidate an agreement or argument. [ 1913 Webster ]

adj. deprived of legal force.
Syn. -- nullified. [ WordNet 1.5 ]

adj. tending to invalidate or prove false.
Syn. -- disconfirming. [ WordNet 1.5 +PJC ]

n. The act of inavlidating, or the state of being invalidated. [ 1913 Webster ]

So many invalidations of their right. Burke. [ 1913 Webster ]

‖n. [ F. ] See Invalid, n. [ 1913 Webster ]

n. The condition of an invalid; sickness; infirmity. [ 1913 Webster ]

n. [ Cf. F. invalidité, LL. invaliditas lack of health. ] [ 1913 Webster ]

1. Lack of validity or cogency; lack of legal force or efficacy; invalidness; as, the invalidity of an agreement or of a will. [ 1913 Webster ]

2. Lack of health; infirmity. [ Obs. ] Sir W. Temple. [ 1913 Webster ]

n. Invalidity; as, the invalidness of reasoning. [ 1913 Webster ]

a. Not valorous; cowardly. [ 1913 Webster ]

a. Valuable beyond estimation; inestimable; priceless; precious. [ 1913 Webster ]

adv. Inestimably. Bp. Hall. [ 1913 Webster ]

a. Inestimable. [ R. ] Drayton. [ 1913 Webster ]

n. [ Cf. F. invariabilité. ] The quality of being invariable; invariableness; constancy; uniformity. [ 1913 Webster ]

a. [ Pref. in- not + variable: cf. F. invariable. ] Not given to variation or change; unalterable; unchangeable; always uniform. [ 1913 Webster ]

Physical laws which are invariable. I. Taylor.

-- In*va"ri*a*ble*ness, n. -- In*va"ri*a*bly, adv. [ 1913 Webster ]

n. (Math.) An invariable quantity; a constant. [ 1913 Webster ]

adv. Always; in every case. [ PJC ]

n. (Math.) The property of remaining invariable under prescribed or implied conditions. J. J. Sylvester. [ 1913 Webster ]

n. (Math.) An invariable quantity; specifically, a function of the coefficients of one or more forms, which remains unaltered, when these undergo suitable linear transformations. J. J. Sylvester. [ 1913 Webster ]

n. [ L. invasio: cf. F. invasion. See Invade. ] [ 1913 Webster ]

1. The act of invading; the act of encroaching upon the rights or possessions of another; encroachment; trespass. [ 1913 Webster ]

2. A warlike or hostile entrance into the possessions or domains of another; the incursion of an army for conquest or plunder. [ 1913 Webster ]

3. The incoming or first attack of anything hurtful or pernicious; as, the invasion of a disease.

Syn. -- Invasion, Irruption, Inroad. Invasion is the generic term, denoting a forcible entrance into a foreign country. Incursion signifies a hasty and sudden invasion. Irruption denotes particularly violent invasion. Inroad is entry by some unusual way involving trespass and injury. [ 1913 Webster ]

a. [ LL. invasivus: cf. F. invasif. See Invade. ] 1. Tending to invade; characterized by invasion; aggressive. “Invasive war.” Hoole. [ 1913 Webster ]

2. (Med.) tending to spread, especially tending to intrude into healthy tissue; -- used mostly of tumors. [ Narrower terms: malignant ] PJC ]