suit (n.) Look up suit at Dictionary.com
c.1300, sute, also suete, suite, seute, "a band of followers; a retinue, company;" also "set of matching garments" worn by such persons, "matching livery or uniform;" hence " kind, sort; the same kind, a match;" also "pursuit, chase," and in law, "obligation (of a tenant) to attend court; attendance at court," from Anglo-French suit, siwete, from Old French suite, sieute "pursuit, act of following, hunt; retinue; assembly" (12c., Modern French suite), from Vulgar Latin *sequita, fem. of *sequitus, from Latin secutus, past participle of sequi "to attend, follow" (see sequel).

Legal sense of "lawsuit; legal action" is from mid-14c. Meaning "the wooing of a woman" is from late 15c. Meaning "set of clothes to be worn together" is attested from late 14c., also "matching material or fabric," from notion of the livery or uniform of court attendants. As a derisive term for "businessman," it dates from 1979. Meaning "matched set of objects, number of objects of the same kind or pattern used together" is from late 14c., as is that of "row, series, sequence." Meaning "set of playing cards bearing the same symbol" is first attested 1520s, also ultimately from the notion of livery. To follow suit (1670s) is from card-playing: "play a card of the same suit first played," hence, figuratively, "continue the conduct of a predecessor."
suit (v.) Look up suit at Dictionary.com
"be agreeable or convenient, fall in with the views of," 1570s, from suit (n.), perhaps from the notion of "join a retinue clad in like clothes." Earlier "seek out" (mid-15c.); "be becoming" (mid-14c.). Meaning "make agreeable or convenient" is from 1590s. Meaning "provide with clothes" is from 1570s; that of "dress oneself" is from 1590s; with up (adv.) from 1945. Expression suit yourself attested by 1851. Related: Suited; suiting.