parallel (adj.)

1540s, in geometry, of lines, "lying in the same plane but never meeting in either direction;" of planes, "never meeting, however far extended;" from French parallèle (16c.) and directly from Latin parallelus, from Greek parallēlos "parallel," from para allēlois "beside one another," from para- "beside" (see para- (1)) + allēlois "each other," from allos "other" (from PIE root *al- "beyond"). Figurative sense of "having the same direction, tendency, or course" is from c. 1600.

As a noun from 1550s, "a line parallel to another line." Meanings "a comparison made by placing things side by side" and "thing equal to or resembling another in all particulars" are from 1590s.  Parallel bars as gymnastics apparatus is recorded from 1868.

parallel (v.)

1590s, transitive, "place in position parallel to something else," from parallel (n.). Meaning "make closely similar to something else" is from 1620s; intransitive sense of "be like or equal, agree" is from 1620s.

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Definitions of parallel from WordNet
parallel (v.)
be parallel to;
Their roles are paralleled by ours
parallel (v.)
make or place parallel to something;
They paralleled the ditch to the highway
Synonyms: collimate
parallel (v.)
duplicate or match;
Synonyms: twin / duplicate
parallel (n.)
something having the property of being analogous to something else;
Synonyms: analogue / analog
parallel (n.)
an imaginary line around the Earth parallel to the equator;
Synonyms: latitude / line of latitude / parallel of latitude
parallel (n.)
(mathematics) one of a set of parallel geometric figures (parallel lines or planes);
parallels never meet
parallel (adj.)
being everywhere equidistant and not intersecting;
dancers in two parallel rows
concentric circles are parallel
parallel lines never converge
parallel (adj.)
of or relating to the simultaneous performance of multiple operations;
parallel processing