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