INTENTION, concentration of attention or gaze.
INTENTIVE, attentive.
INTERESSED, implicated.
INTRUDE, bring in forcibly or without leave.
INVINCIBLY, invisibly.
INWARD, intimate.
IRPE (uncertain), "a fantastic grimace, or contortion of the body: (Gifford)."
JACK, Jack o' the clock, automaton figure that strikes the hour; Jack-a-lent, puppet thrown at in Lent.
JACK, key of a virginal.
JACOB'S STAFF, an instrument for taking altitudes and distances.