A sickle is a curved, hand-held agricultural tool typically used for harvesting cereal crops or cutting grass for hay. The inside of the curve is the cutting edge, and is serrated.

The farm-hand swings the blade against the base of the crop, cutting through the stems with a sawing action.

The sickle was superseded in the nineteenth century by the scythe which was more comfortable and by mechanised combine-harvesters and tractor machinery.

Pitt Rivers Museum, Oxford

The smooth-edged hook succeeded the serrated sickle for reaping corn in many places about 1860-1870. Fagging tools have sharp blades and are heavier and wider than sickles and used with a different action.

Instead of grasping the corn, the reaper held back the stalks or drew them towards him with a short crook called a fagging stick and slashed through the straw rather than sawing it as with a sickle.

A larger quantity of corn was cut at one swing, though time was taken up with sharpening the blade. The hooks are still used today for trimming hedges and cutting crops close to hedges or walls that cannot be reached by machine.

According to the Museum of English Rural Life at Reading

This may be the origin of the phrase, 'By hook or by crook.'

Billhooks - these were and still are mainly used for pruning and lopping branches and other vegetation and are particularly useful for hedging. The design, size and shape vary widely depending on what they're going to be used for, as well as local variations.

Finch Foundry, Sticklepath