Bubble bath initially about 45 inches in days of old (4)
I believe the answer is:
bell
'bubble' is the definition.
(bell can mean a bubble in liquid)
'bath initially about 45 inches in days of old' is the wordplay.
'initially' suggests taking the first letters.
'about 45 inches in days of old' becomes 'ell' (historical unit for measuring fabric).
The initial letter of 'bath' is 'b'.
'b'+'ell'='BELL'
(Other definitions for bell that I've seen before include "He invented" , "kind of curve" , "Metal ringer" , "Stag's cry; ringer" , "Tinkler" .)