C

• celsius

  General

• Central Standard Time (time groups only)

  Weather

• centre (runway ID)

  ICAO

• circling (approach and landing charts)

  ATC

• continental (air mass)

  Weather

C has 5 meanings; the right one depends on context. A weather report, a NOTAM or an ATC clearance. Got a NOTAM full of contractions? Paste it into the decoder.

Source: FAA Order JO 7340.2 Contractions. Not for operational use.