index--indexes (to books), indices (signs in algebra).

pea--peas (separately), pease (collectively).

penny--pennies (separately), pence (collectively).

shot--shot (collective balls), shots (number of times fired).

In speaking of coins, _twopence_, _sixpence_, etc., may add _-s_,
making a double plural, as two _sixpences_.


[Sidenote: _One plural, two meanings._]

49. Other words have one plural form with two meanings,--one
corresponding to the singular, the other unlike it.

custom--customs: (1) habits, ways; (2) revenue duties.

letter--letters: (1) the alphabet, or epistles; (2) literature.

number--numbers: (1) figures; (2) poetry, as in the lines,--

I lisped in _numbers_, for the numbers came.--POPE.

Tell me not, in mournful _numbers_.--LONGFELLOW.

_Numbers_ also means issues, or copies, of a periodical.

pain--pains: (1) suffering; (2) care, trouble,