1 on loan
2 on one's own
3 on one's way to
4 on purpose
5 on sale
6 on short notice
7 on the dot
8 on the right track
9 on the side
10 on the tip of one's tongue
1 on the whole
2 on time
3 on top of
4 once and for all
5 once every other…
6 once in a while
7 once more
8 one day is as good as the next
9 one in a million
10 one step at a time
1 open a savings account
2 or so
3 or something
4 oral presentation
5 order sth. From a catalog
6 order through mail
7 organic chemistry
8 other than
9 out of bounds
10 out of breath
2 on one's own
3 on one's way to
4 on purpose
5 on sale
6 on short notice
7 on the dot
8 on the right track
9 on the side
10 on the tip of one's tongue
1 on the whole
2 on time
3 on top of
4 once and for all
5 once every other…
6 once in a while
7 once more
8 one day is as good as the next
9 one in a million
10 one step at a time
1 open a savings account
2 or so
3 or something
4 oral presentation
5 order sth. From a catalog
6 order through mail
7 organic chemistry
8 other than
9 out of bounds
10 out of breath