"his first wife"

• never previously done or occurring

  "her first day at school"

• coming or encountered next after a specified or implied time, event, etc.

  "the first house I came to"

• before doing something else specified or implied

  "Do you mind if I take a shower first?"

• for the first time

  "she first picked up a guitar out of sheer boredom"

• the first occurrence of something notable

  "we travelled by air, a first for both of us"

• the first in a sequence of a vehicle's gears

  "he stuck the car in first and revved"

• first base

  "he made it all the way home from first"

• the first form of a school or college
• a first edition of a book

  "collectors of modern firsts"

"the doctor's first duty is to respect this right"

• the most pressing, likely, or suitable

  "he is the first to admit he was not the best of patients"

• firstly; in the first place (used to introduce a main point or reason)

  "first, it is wrong that the victims should have no remedy"

• in preference; rather (used when strongly rejecting a suggestion or possibility)

  "she longed to go abroad, but not at this man's expense—she'd die first!"

• the first finisher or position in a race or competition
• performing the highest or chief of two or more parts for the same instrument or voice

  "the first violins"

• having precedence over all others of a similar kind

  "First Lord of the Admiralty"

• a place in the top grade in an examination, especially that for a degree

  "chaps with firsts from Oxbridge"

• a person who has received the top grade in an examination for a degree
• the best or main team of a sports club

  "he was asked to play for the firsts"

• goods of the best quality

  "factory firsts, seconds, and discontinued styles"

"the car plunged nose first into the river"