The Collaborative International Dictionary of English v.0.48:

Compiler \Com*pil"er\ (k[o^]m*p[imac]l"[~e]r), n. [OE.
   compiluor; cf. OF. compileor, fr. L. compilator.]
   1. One who compiles; esp., one who makes books by
      compilation.
      [1913 Webster]

   2. (Computers) a computer program that decodes instructions
      written in a higher-level computer language to produce an
      assembly-language program or an executable program in
      machine language.
      [WordNet 1.5 +PJC]

WordNet (r) 3.0 (2006):

compiler
    n 1: a person who compiles information (as for reference
         purposes)
    2: (computer science) a program that decodes instructions
       written in a higher order language and produces an assembly
       language program [syn: compiler, compiling program]

The Free On-line Dictionary of Computing (30 December 2018):

compiler

    A program that converts another program
   from some source language (or programming language) to
   machine language (object code).  Some compilers output
   assembly language which is then converted to machine
   language by a separate assembler.

   A compiler is distinguished from an assembler by the fact that
   each input statement does not, in general, correspond to a
   single machine instruction or fixed sequence of instructions.
   A compiler may support such features as automatic allocation
   of variables, arbitrary arithmetic expressions, control
   structures such as FOR and WHILE loops, variable scope,
   input/ouput operations, higher-order functions and
   portability of source code.

   AUTOCODER, written in 1952, was possibly the first primitive
   compiler.  Laning and Zierler's compiler, written in
   1953-1954, was possibly the first true working algebraic
   compiler.

   See also byte-code compiler, native compiler, optimising
   compiler.

   (1994-11-07)