Bacterial infection you once discovered by the way (4)
I believe the answer is:
stye
'bacterial infection' is the definition.
'stye' can be an answer for 'infection' (stye is a kind of infection). I'm unsure of the 'bacterial' bit.
'you once discovered by the way' is the wordplay.
'you once' becomes 'ye' (archaic version of 'you').
'discovered by' means one lot of letters go next to another.
'the way' becomes 'st' (abbreviation for street).
'ye' after 'st' is 'STYE'.
Can you help me to learn more?
(Other definitions for stye that I've seen before include "Viewer's complaint" , "dump" , "Infected swelling of the eye" , "makes viewer sore" , "Tamworth residence" .)