to be very healthy or working well.

She was in fine fettle when she came back from her trip to the States.

The business is in fine fettle and we're even planning to expand.

• on the fence
• on the firing line
• on the fly
• on the fritz
• on the front burner
• on the front line of
• on the front line of something
• on the front lines of
• on the front lines of something
• on the heels of
• on the heels of something
• on the hoof
• on the horizon
• on the horns of a dilemma
• on the hour
• on the house
• on the job
• on the lam
• on the level
• on the line
• on the loose
• on the margins of
• on the margins of something
• on the market
• on the mend