Using wn.synset('dog.n.1').lemma_names is the correct way to access the synonyms of a sense. It's because a word has many senses and it's more appropriate to list synonyms of a particular meaning/sense. To enumerate words with similar meanings, possibly you can also look at the hyponyms.
Sadly, the size of Wordnet is very limited so there are very few lemma_names available for each senses.
Using Wordnet as a dictionary/thesarus is not very apt per se, because it was developed as an inventory of sense/meaning rather than a inventory of words. However you can use access the a particular sense and several (not a lot) related words to the sense. One can use Wordnet as a:
Dictionary: given a word, what are the different meaning of the word
for i,j in enumerate(wn.synsets('dog')):
print "Meaning",i, "NLTK ID:", j.name
print "Definition:",j.definition
Thesarus: given a word, what are the different words for each meaning of the word
for i,j in enumerate(wn.synsets('dog')):
print "Meaning",i, "NLTK ID:", j.name
print "Definition:",j.definition
print "Synonyms:", ", ".join(j.lemma_names)
print
Ontology: given a word, what are the hyponyms (i.e. sub-types) and hypernyms (i.e. super-types).
for i,j in enumerate(wn.synsets('dog')):
print "Meaning",i, "NLTK ID:", j.name
print "Hypernyms:", ", ".join(list(chain(*[l.lemma_names for l in j.hypernyms()])))
print "Hyponyms:", ", ".join(list(chain(*[l.lemma_names for l in j.hyponyms()])))
print
[Ontology Output]
Meaning 0 NLTK ID: dog.n.01
Hypernyms words domestic_animal, domesticated_animal, canine, canid
Hyponyms puppy, Great_Pyrenees, basenji, Newfoundland, Newfoundland_dog, lapdog, poodle, poodle_dog, Leonberg, toy_dog, toy, spitz, pooch, doggie, doggy, barker, bow-wow, cur, mongrel, mutt, Mexican_hairless, hunting_dog, working_dog, dalmatian, coach_dog, carriage_dog, pug, pug-dog, corgi, Welsh_corgi, griffon, Brussels_griffon, Belgian_griffon
Meaning 1 NLTK ID: frump.n.01
Hypernyms: unpleasant_woman, disagreeable_woman
Hyponyms:
Meaning 2 NLTK ID: dog.n.03
Hypernyms: chap, fellow, feller, fella, lad, gent, blighter, cuss, bloke
Hyponyms:
Meaning 3 NLTK ID: cad.n.01
Hypernyms: villain, scoundrel
Hyponyms: perisher
