prep.
       - expressing direction or position in relation to a location, point, or condition. 
▸chiefly Brit. (in telling the time) before (the hour specified).
 - identifying the person or thing affected.
 - identifying a relationship between one person or thing and another. 
▸indicating a rate of return:
 ten miles to the gallon.
 - indicating that two things are attached.
 - governing a phrase expressing someone's reaction:
 to her astonishment, he smiled.
 - used to introduce the second element in a comparison.
 - placed before a debit entry in accounting.
 
infinitive marker
  - used with the base form of a verb to indicate that the verb is in the infinitive. 
▸
(about to)
 forming a future tense with reference to the immediate future.
 - used without a verb following when the missing verb is clearly understood:
 she said she didn't want to.
 
adv.
 so as to be closed or nearly closed.
 
  Etymology
  OE tō (adv. and prep.), of W. Gmc origin.