As an adjective courteous

is showing regard or thought for others; especially, displaying good manners or etiquette.

As an adverb uncourteously is

in a way that is not courteous impolitely.

Reoccurring is a alternative form of reoccuring.

As verbs the difference between reoccuring and reoccurring

is that reoccuring is misspelling of lang=en while reoccurring is present participle of lang=en.

Reoccured is an alternative form of reoccurred.

As verbs the difference between reoccured and reoccurred

is that reoccured is while reoccurred is (reoccur).

In grammar terms the difference between imperfectiveness and perfectiveness

is that imperfectiveness is the state or quality of being imperfective while perfectiveness is the state or quality of being perfective.

As nouns the difference between schedule and rescheduling

is that schedule is a slip of paper; a short note while rescheduling is a change of schedule.

As verbs the difference between schedule and rescheduling

is that schedule is to create a time-schedule while rescheduling is present participle of lang=en.

As verbs the difference between modifying and retooling

is that modifying is altering while retooling is .

As a noun retooling is

the fact or process of re-equipping or modifying something.

As nouns the difference between scythian and scyth

is that scythian is an inhabitant of Scythia, an ill-defined region centered in southern Russia while Scyth is a Scythian.

As an adjective Scythian

is relating to Scythia or Scythians.

As a proper noun Scythian

is the Eastern Iranian language of Scythians.

As nouns the difference between propeller and propfan

is that propeller is propeller while propfan is a modified turbofan engine with the propeller outside the engine duct of an aircraft.

As nouns the difference between duct and propfan

is that duct is a pipe, tube or canal which carries gas or liquid from one place to another while propfan is a modified turbofan engine with the propeller outside the engine duct of an aircraft.

As a verb duct

is to channel something through a duct (or series of ducts.

As nouns the difference between aircraft and aerostructure

is that aircraft is a vehicle capable of atmospheric flight due to interaction with the air, such as buoyancy or lift while aerostructure is any component or subsystem of the airframe of an aircraft.