ETYM Local, U. S.
(Alternate spelling: itemise).
1. To state in items, or by particulars.
2. In income taxes, to list deductible expenses, as opposed to taking a standard deduction.

Alternate (chiefly British) spelling of particularize.

(Alternate spelling: particularise).
To give as a particular, or as the particulars; to mention particularly; to give the particulars of; to enumerate or specify in detail.

1. To be specific about; SYN. particularize, specialize.
2. To decide upon, as of variables in math; SYN. set, determine, fix.
3. To determine the essential quality of; SYN. define, delineate, delimit, delimitate.