long
short
thick
fine, thin
faint
a faint white line

direct, straight
curved, jagged, wavy, zigzag
diagonal, horizontal, parallel, perpendicular, vertical
continuous, solid, unbroken
broken, dashed (AmE), dotted
Sign on the dotted line.

finish (AmE), finishing (BrE), starting (all sports)
free-throw (AmE), goal (both sports)
The ball bounced off the crossbar and fell behind the goal line.

contour
boundary, state (AmE)
the boundary line between two countries
His family lived across the state line in West Virginia.

centre/center
She crossed the centre/center line and hit an oncoming truck.

draw, mark

run
divide sth, separate sth
connect sth
The pencil line connects one box to another.

correspond to sth, denote sth, depict sth, indicate sth, mark sth, represent sth, show sth
Horizontal lines indicate the time spent executing the program.

in a line
Walk in a straight line.

a line of latitude, a line of longitude

long, short
new
continuous

form

in a/the line
The soldiers stood in a line.

on a/the line
Start each paragraph on a new line.

long, short
checkout, lunch
supermarket checkout lines
The lunch line was long as usual.

form

in line
You'll have to wait in line like everybody else.

direct, trunk
power, transmission, utility (AmE)
sewer (AmE)
fuel, gas (both AmE)
There were two fuel lines coming into the engine.

phone, telephone
DSL
fax
outside, party, private
What do I dial for an outside line?

hold
Hold the line (= Don't put the receiver down), please.

be busy (AmE), be engaged (BrE)
be dead, go dead

down the line
He kept shouting down the line at me.

on the line
It's your mother on the line (= on the telephone).

on line (usually online) (= connected to a computer system)

rail (AmE), railway (BrE), train
subway (AmE), underground (esp. BrE)
main
branch (esp. BrE), commuter, trunk
The branch line is threatened with closure.

take
Take the green line and change at the first stop.

on a/the line
We live on the Northern Line. (BrE)

the end of the line

learn, practise/practice
recite, say
forget
flub (AmE), fluff (esp. BrE), mess up (esp. AmE)
miss

worry
deep
Deep lines ran from her nose to her mouth.

faint
I saw the faint lines of concern etched into his brow.

have
He has lines on his forehead.

run
appear
Deep worry lines had appeared on her forehead.

broad
The broad lines of company policy are already laid down.

firm, hard, strong, tough
official, party, political

adopt, follow, pursue, take
fall into
The actions of investors do not always fall into line with financial theory.

bring sb/sth into
The other members of the board must be brought into line.

in line with (= in agreement with), out of line with (= not in agreement with)
out of line with party policies

line on
the official line on food safety

a line of argument, a line of reasoning
There's a problem with this line of reasoning.

a line of attack
Our approach involves two main lines of attack.

a line of enquiry/inquiry, a line of investigation, a line of questioning
a line of thought
This line of thought perturbs me.

a line of evidence (esp. AmE)
multiple lines of evidence all leading to the same conclusion

battle, defensive, firing, front, offensive (AmE)
The middle managers were in the firing line of job cuts. (figurative)

behind enemy lines
in the front line, on the front line
line of defence/defense
We know that intelligence is our first line of defence/defense against terrorism.