One of three little outings? (7)

I believe the answer is:

triplet

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'one of three' is the definition.
(I've seen this before)

I don't understand the remainder of the clue.

(Other definitions for triplet that I've seen before include "Not the only baby in the group" , "one arriving with two others" , "One of a group of three" , "One of a set of three" , "One of a small group" .)

I've seen this clue in the Evening Standard.

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