"weasel-like; pertaining to weasels," 1650s, from Latin mustelinus "of or belonging to weasels," from mustela; see mustelid + -ine (1).

early 14c., moustren, "to display, reveal, to show or demonstrate" (senses now obsolete), also "to appear, be present," from Old French mostrer "appear, show, reveal," also in a military sense (10c., Modern French montrer), from Latin monstrare "to show," from monstrum "omen, sign" (see monster).

The transitive meaning "to collect, assemble, bring together in a group or body," especially for military service or inspection, is from early 15c. The intransitive sense of "assemble, meet in one place," of military forces, is from mid-15c. The figurative use "summon, gather up" (of qualities, etc.) is from 1580s.

To muster in (transitive) "receive as recruits" is by 1837; to muster out "gather to be discharged from military service" is by 1834, American English. To muster up in the figurative and transferred sense of "gather, summon, marshal" is from 1620s. Related: Mustered; mustering.

late 14c., moustre, "action of showing, demonstration, manifestation, exhibition" (a sense now obsolete), from Old French mostre "illustration, proof; examination, inspection" (13c., Modern French montre), literally "that which is shown," from mostrer "appear, show, reveal" (see muster (v.)). Meaning "an assembly or act of gathering troops" is from c. 1400. Meaning "a register or roll of troops mustered" is from 1560s. To pass muster "undergo review without censure" is by 1620s; in the form pass the musters it is attested from 1570s.

1520s, "moldy, sour," perhaps a variant of moisty "moist, damp" (see moist), but musty, of bread, "containing must" is attested mid-15c., and from 15c.-19c. must also was a variant of musk. Related: Mustiness.

late 14c., "tendency to change, inconstancy," from Old French mutabilité, from Latin mutabilitas, from mutabilis "changeable" (see mutable).

It is the same!—For, be it joy or sorrow,
    The path of its departure still is free;
Man's yesterday may ne'er be like his morrow;
    Nought may endure but Mutability. 

[Shelley, from "Mutability," 1816]

"agent that causes mutation," 1946, from mutation + -gen "thing that produces." Related: Mutagenic; mutagenesis; mutagenize.

1900 in the biological sense, "individual or form which has arisen by or undergone (genetic) mutation," from Latin mutantem (nominative mutans) "changing," present participle of mutare "to change" (from PIE root *mei- (1) "to change, go, move"). In the science fiction sense, it is attested by 1954. As an adjective from 1903.

1818, "to change state or condition, undergo change," back-formation from mutation. In the genetic sense, "undergo mutation," 1913, from Latin mutatus, past participle of mutare "to change" (from PIE root *mei- (1) "to change, go, move"). Related: Mutated; mutating.