adjective
always used before a noun
alone in a class or category :existing with no other or others of the same kind - usually used with the or a possessive (such as my, her, its, their, John's, etc.)
one of the only
one of very few :one in a small class or category
the only
used to emphasize that a particular person or thing should be the one chosen; usually + for
adverb
no more than
nothing other than - used to indicate that a single thing was done, is needed, is possible, etc.
c - used for emphasis
excluding all others
in no time, place, or situation except the one specified
for no other reason than
nothing more important or serious than
used to emphasize that something happened recently
a - used to say that something has or will have a particular and usually bad result
b - used to indicate something bad or surprising that happens after something else; followed by to + verb
for your eyes only
if only
in name only
not only
used to say that both of two related statements are true
only have eyes for
only too
very or completely
second only to
conjunction
informal :but, however