conj.
     - introducing a conditional clause: 
▸on the condition or supposition that.
 ▸(with past tense) introducing a hypothetical situation.
 ▸every time.
 - despite the possibility that. 
▸despite being.
 - whether.
 - expressing a polite request or tentative opinion.
 - expressing surprise or regret.
 
n.
 a condition or supposition.
 
  Phrase
  
    - if and only if
 used to introduce a condition which is necessary as well as sufficient.  - if anything
 used to suggest tentatively that something may be the case.  - if not
 perhaps even (used to introduce a more extreme term than one first mentioned).  - if only
 even if for no other reason than.  - if so
 if that is the case. 
   
  Etymology
  OE gif, of Gmc origin.