I. verb
1.
Synonyms: keep 5, detain, hold, hold back, keep back, keep out, retain, withhold
2.
to set or have set aside or apart
reserve a hotel room
Synonyms: bespeak, book, preengage
Related Word: contract, engage, retain
II. noun
something stored or kept available for future use or need
keep a reserve of canned foods on hand
Synonyms: backlog, hoard, inventory, nest egg, reservoir, stock, stockpile, store
Related Word: fund, supply
Idioms: something for a rainy day, something in the sock