On few occasions, in few cases or instances, not often; rarely, infrequently.

(also -whens) rarely.

With ever added pleonastically. (Cf. ever, adv. 5a, rarely, adv. 2)

= seldom, adv.

rarely.

rarely.

rarely.

= thinly, adv. 2.

= rarely, adv. (esp. in sense 2). Chiefly poetic.

= seldom, adv. adj. Also sendle-times = seldom-times.

Rarely, sparingly. Obsolete. (Cf. dainty, adj. 2.)

With large intervals of space or time; sparsely; not closely or thickly.

Seldom, infrequently; in few instances.

once in a moon (also once a moon): once a month; occasionally. See also once in a blue moon at blue moon, n. 2b.

By way of exception; exceptionally.

Rarely.

for once: †(a) (in Old English) certainly, no matter what (obsolete rare); (b) on this occasion, if on no other. Also in phrases corresponding to…

With restriction to a few occasions; seldom, infrequently.

Seldom, scarcely ever, rarely. Obsolete.

(un-, prefix1 affix 5 Usually with preceding negative.)

Infrequently, seldom.

Not frequently; somewhat rarely, seldom. Now chiefly in not infrequently = rather frequently.

once in a while (occasionally once and a while): from time to time; very occasionally (see also every, adj. pron.phrases 3c). once in a way: see way…

In isolated cases or instances.

At rare or infrequent intervals of time. rare.

rarely.

(for) once in a way: on this occasion, if on no other; for once; (also in weaker sense) rarely, exceptionally; once in a while.