Stain one's pants touring India (5)
I believe the answer is:
eosin
'stain' is the definition.
Both the answer and definition are singular nouns.
Maybe you can see an association between them that I can't see?
'one's pants touring india' is the wordplay.
'pants' is an anagram indicator (UK informal term for 'nonsense' or 'rubbish').
'touring' means one lot of letters goes inside another (touring can mean going round).
'india' becomes 'i' (phonetic alphabet: alpha, bravo, charlie etc.).
'ones' with letters rearranged gives 'eosn'.
'eosn' going around 'i' is 'EOSIN'.
Can you help me to learn more?
(Other definitions for eosin that I've seen before include "Red dyestuff" , "Red dye" .)