mid-14c., "act of chopping, cutting with a quick blow," from chop (v.1). Meaning "piece cut off" is mid-15c.; specifically "slice of mutton, lamb, or pork" (usually cut from the loin and containing the rib) is from 1630s, probably from being "chopped" from the loin. Sense of "a blow, strike" is from 1550s. Specific cricket/baseball sense of "a downward stroke with the bat" is by 1888.
1620s, "a sentinel," agent noun from round (n.) in the "circuit performed by a sentinel" sense, on the notion of "one who makes the rounds." Sense of "chronic loafer, drunkard, or criminal" is by 1854, American English, on notion of one who "goes the round" of misdemeanor, arrest, trial, imprisonment, and release. Rounders, a baseball-like game in England played with a small bat, is attested by that name from 1828, from the player "rounding" the bases after the ball is hit.
"late in occurrence or development," 1590s, from French sérotine, from Latin serotinus "that which comes late; that which happens in the evening," from sero, adverb of serus "late" (see soiree). Chiefly used of late-flowering plants. Also as a noun, a type of small, brown bat, from 1771. Related: serotinous, 1880, in botany, "appearing later in the season than usual" (Blount, 1656, has it as "that is in the evening, late, lateward"); serotinal.
1690s, "curved line, a continuous bending without angles," from curve (v.). With reference to the female figure (usually plural, curves), from 1862; in reference to statistical graphs, by 1854; as a type of baseball pitch that does not move in a straight line, from 1879. An old name for it was slow. "Slows are balls simply tossed to the bat with a line of delivery so curved as to make them almost drop on the home base." [Chadwick's Base Ball Manual, 1874]
late 14c., "hurt, harm, injury, pain;" also "breach of the law, wrongdoing; transgression against God, sin;" also "the causing of displeasure, act or fact of wounding the feelings of or displeasing another;" also "displeasure, annoyance, umbrage," from Old French ofense "offense, insult, wrong" (13c.) and directly from Latin offensa "an offense, injury, affront, crime," literally "a striking against," noun use of fem. past participle of offendere (see offend).
Meaning "action of attacking" is from c. 1400. Sporting sense of "the team on the attack, at bat, with the ball," etc. is by 1894.
BOATSWAIN. The warrant officer who in the old Navy was responsible for all the gear that set the ship in motion and all the tackle that kept her at rest. [Sir Geoffrey Callender, "Sea Passages," 1943]
He also summons the hands to their duties with a silver whistle. Phonetic spelling bo'sun/bosun is attested from 1840. Fowler  writes, "The nautical pronunciation (bō'sn) has become so general that to avoid it is more affected than to use it."