Narrow gauge train set spread out (8)

I believe the answer is:

straiten

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'narrow gauge' is the definition.
'straiten' can be an answer for 'narrow' (thesaurus). I'm not certain of the 'gauge' bit.

'train set spread out' is the wordplay.
'spread out' indicates anagramming the letters (I've seen 'spreading out' mean this).
'train'+'set'='trainset'
'trainset' is an anagram of 'STRAITEN'.

Can you help me to learn more?

(Other definitions for straiten that I've seen before include "Train set (anag.)" , "Limit" , "Restrict" , "distress" .)

I've seen this clue in The Globe and Mail.

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