1. In compound words

a. The words that are names of "Road" [Yol] [transportation] are written seperately.

    Çevre yolu = peripheral highway

    Kara yolu   = Highway

    Deniz yolu  = Seaway, Sea route.

    Hava yolu   = Airway, Air route.

b. Space objects  that are in compound form must be written seperately;

Çoban Yıldızı = lodestar

Kutup Yıldızı = polar star

Kuy­ruklu Yıldız = stray comet

gök taşı  =  Meteorite

c. Organ names in body that are in compound forms must be written seperately.

elmacık kemiği;

serçe parmak,

şehadet par­mağı

yüzük parmağı

azı dişi,

köpek dişi,

süt dişi;

kuyruk sokumu,

safra kesesi;

d. Some time expressions that are in compound forms must be written seperately ;

gece yarısı --> midnight

gün or­tası  ---> midday

hafta başı ----> begining of the week [the first day of the week]

hafta sonu ----> weekend

2 . The intensified [over emphasized] words must be written as One word.

Dümdüz ---> Very straight [Straight ahead]

çırılçıplak ---> starkers [naked as a jaybird]

sapsarı  ---> Very yellow

kapkara  ----> jet black, Very black

büsbütün ------> altogether, entirely

3. The copulative verbs [ idi, imiş, ise ] can be written  seperately as well as one word [suffixed to the word ]

a. When they suffixed to the words that end with a consonant the vowel "i" drops and follows the vowel harmony ;

yorgun-du (yorgun idi)  ---> He/she/it  was tired.

güzel-miş [güzel imiş] -----> [I heard that, I was told that ] he/she/ it was beautiful.

gelir-se (gelir ise)  ----> If  he/she/it comes

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b. When they suffixed to the words that end with a vowel they take buffer "y" and "i" in copulative verbs drop and follows the vowel harmony.

sonuncu-y-du (sonuncu idi)

yabancı-y-mış [yabancı imiş]

ne-y-se (ne ise) 

4. " İken " which is an adverbial form of copulative verb can be attached onto the word or can be written seperately.

a. when attached onto the word "i" drops ;

çalışıyor-ken (çalışıyor iken)  ---> while [when] studying

okur-ken (okur iken)           -----> while [when] reading

uyur-ken (uyur iken)

yazar-ken (yazar iken)

geliyor-ken (geliyor iken)

öğretmen-ken (öğretmen iken)

What about baş-? It has an independent meaning ´head´ but it is often written as one word in compounds like

                    başbakan

                    başkent

                    başparmak

and there is even no POSS in the end.

5. When infinitives that end with -me,-ma takes -a / -e, -ı / -i  suffixes, the buffer "y" comes between them.

çalışma-y-a

darılma-y-ı

kalaylama-y-a

okuma-y-a

görme-y-i

gülme-y-i

sevme-y-e

silme-y-i

It should refer an ´organ´ başbakan and başkent do not refer an organ. When it comes to "başparmak " that must be exception I believe.