unique; individual; original; unusual
collision; crash; running into; conflict; quarrel; clashing
detection; sense (e.g. sensor)
security hole; vulnerability
to get help; to enlist aid
before one knows it; before one realises; without one's knowledge; without noticing
immediately; right away; on the spot
thread (of execution); thread (on an Internet forum, mailing list, etc.); topic; conversation
carelessly; thoughtlessly; inadvertently
to step on; to tread on; to set foot on (e.g. foreign soil); to stand on; to experience; to undergo; to follow (rules, principles, etc.)
speed; velocity; pace; velocity
several times (as large, over)
unreasonable; unnatural; impossible; forcible; forced; excessive (work, etc.); immoderate
prosperous; flourishing; popular; widespread; active; lively
contribution (furthering a goal or cause); services (to a cause)
complex sentence; sentence with an independent clause and at least one dependent clause
sometimes; occasionally; now and then; from time to time
formation; establishment; conclusion (e.g. of a deal); reaching (e.g. an agreement); being valid (of a theory, argument, etc.); holding
to forget; to leave carelessly; to be forgetful of; to forget about; to forget (an article)
stipulation; prescription; provision; regulation; rule
six; six years of age; six o'clock (old time system)
publication; issue (of journal, newspaper, etc.); issue (of banknotes, bonds, passport, etc.); raising an event (software)
to protect; to guard; to defend; to keep (i.e. a promise); to abide (by the rules); to observe
probability; likelihood; chances
to fall down; to drop; to be omitted; to be missing; to decrease; to sink; to fail (e.g. exam or class)
riddle; puzzle; enigma; enigmatic; mysterious
adjustment; regulation; coordination; reconciliation; tuning; fixing
abruptly; suddenly; all of a sudden; without warning
side (of something, or taking someone's side); part; (watch) case
present condition; existing state; status quo; current state
when it comes to ...; if one were to speak of ...; by ... you mean ...; when you say ... you mean that ...; whenever ...; if it's ... then (without fail)
if so; in that case; in that situation