The Collaborative International Dictionary of English v.0.48:

Milli- \Mil"li-\ (m[i^]l"l[i^]-). [From L. mille a thousand.]
   (Metric System, Elec., Mech., etc.)
   A prefix denoting a thousandth part of; as, millimeter,
   milligram, milliamp[`e]re.
   [1913 Webster]

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

prefix
atto-
exa-
femto-
giga-
kilo-
mega-
micro-
milli-
peta-
pico-
tera-
yocto-
yotta-
zepto
zetta-

   1.  An SI prefix used to multiply the value of an SI
   (Système International) unit by some power of ten.

   2.  In mathematics or programming, a
   prefix operator is one that is written before its operand.  In
   a programming language using prefix notation, all operators
   are prefix operators.

   (2014-07-08)