considerably, significantly
The gap between the candidates has narrowed significantly.

a little, slightly, etc.
The river narrows a little here.
The trade deficit with China narrowed slightly.

dramatically, sharply
The gap between the two parties narrowed sharply in the days before the election.

gradually
Left untreated, the arteries will gradually narrow, restricting the flow of blood.

to
By the final round the gap had narrowed to three votes.

slightly
Her eyes narrowed slightly as she studied the woman.

suddenly
dangerously, suspiciously
His blue eyes narrowed suspiciously.

against
Lee's eyes narrowed against the harsh glare of the sun.

at
His eyes suddenly narrowed at the sight of her.

in
Her eyes narrowed in anger.

to
His eyes narrowed to slits.

with
His eyes narrowed with suspicion.

Narrow is used with these nouns as the subject:
deficit, divide, eye, gap, gaze, margin, path, road

Narrow is used with these nouns as the object:
artery, choice, deficit, divide, eye, focus, gap, horizon, list, scope, search

be, look, seem
become, get

extremely, fairly, very, etc.
The pass gets extremely narrow at its eastern edge.

a little, slightly, etc.
The rear part of the casing is slightly narrower than the front.

relatively

be, seem
become

extremely, fairly, very, etc.
increasingly
a little, slightly, etc.
comparatively, relatively

in
people who are rather narrow in outlook

Narrow is used with these nouns:
agenda, alley, angle, base, beam, belt, bench, border, bridge, category, channel, chest, chimney, circle, clientele, conception, confines, context, corridor, crack, curriculum, defeat, definition, door, doorway, entrance, escape, eye, flight, focus, foot, gap, gate, gauge, groove, hall, hallway, hip, horizon, ideology, interest, interpretation, lane, lapel, lead, ledge, limit, majority, margin, nose, objective, opening, pass, passage, path, pavement, pelvis, perspective, range, ribbon, river, road, room, scope, seam, self-interest, sense, shaft, shoulder, sidewalk, slice, space, spectrum, stair, staircase, stance, strait, strap, street, stretch, strip, stripe, stroke, topic, track, trail, trench, tube, tunnel, valley, victory, view, vision, vote, waist, width, win, window, wing, zone