1.
If a situation or agreement is ~ on something, it will only happen or continue if this thing happens.
Their support is ~ on his proposals meeting their approval.
...a ~ offer.
ADJ: oft ADJ on n/-ing
~ly
Mr Smith has ~ly agreed to buy a shareholding in the club.
ADV: ADV with v
2.
In grammar, a ~ clause is a subordinate clause which refers to a situation which may exist or whose possible consequences you are considering. Most ~ clauses begin with ‘if’ or ‘unless’, for example ‘If that happens, we’ll be in big trouble’ and ‘You don’t have to come unless you want to’.
ADJ: ADJ n