College in Vilnius periodically recalled (3)
I believe the answer is:
uni
'college' is the definition.
(short for university)
'vilnius periodically recalled' is the wordplay.
'periodically' indicates alternate letters (letters must be selected 'every so often').
'recalled' says the letters should be written in reverse (to recall can mean to bring something back).
The alternating letters of 'vilnius' are 'inu'.
'inu' back-to-front is 'UNI'.
'in' acts as a link.
(Other definitions for uni that I've seen before include "Third-level college, in short" , "Reading is one" , "Seat of learning" , "academic establishment" , "Place of higher education (abbr)" .)